Process for producing on impregnated waterlaid sheet and resultant product

ABSTRACT

A leatherlike sheet material having a low apparent density (high void volume), good internal bond strength, and a slow rate of water pickup is provided by forming a waterlaid sheet containing leather fiber, impregnating the waterlaid sheet with an uncured polyurethane, polyurethane-urea, or polyurea elastomeric resin system, and permitting the uncured resin system to cure in situ. The uncured resin system should be mixed together and quickly brought into contact with the waterlaid sheet, so that little, if any, curing occurs prior to the impregnation step.

United States Patent n 1 Carlson 11 I I 3,708,333 51 Jan. 2, 1973 [54] PROCESS FOR PRODUCING ON IMPREGNATED WATERLAID SHEET AND RESULTANT PRODUCT v 75] inventor? Roiiert causal, Saint Paul,

Minn. 55101 731 Assigns;"manesaa'mnlng aha Manufacturing Co., Saint Paul, Minn.

22 Filed: Oct. 8, 1970 21 Appl.No.: 79,318

[52] US. C1......1l7/140 A, ll7/138.8 UA, 117/142,

117/143 A, 117/161 KP, 117/D1G. 3

[51] Int. Cl ..B32b 27/12, B44d 1/32 [58] Field of Search.....1 17/140 A, 142, DIG. 3, 161

- KP,117/DIG. 7,135.5,143 A, 138.8 UA;

[56] References Cited UNITED STATES PATENTS 3,436,303 4/1969 Raymond et al ..117/140 X 3,282,726 11/1966 Seligsberger ....1 17/142 X 3,102,835 9/1963 White ..117/62.2 X 3,519,478 7/1970 Howell ..117/155 2,774,687 12/1956 Notteboh'm et al ..117/120 3,116,200 12/1963 Young et al. ..106/156 X 2,723,935 11/1955 Rodman ..117/140 x 2,769,712 11/1956 Wilson ..162/151 3,384,506 5/1968 Elkin ..117/141 x 2,977,330 3/l96l Brower ..260/77.5 ux 3,296,016 1/1967 Murphy ..117/140 x FOREIGN PATENTS 0R APPLICATIONS I 511,423 l2/l9s3 Belgium ..1l7/D1G. 3

Primary Examiner-William D. Martin Assistant Examiner--l-larry J. Gwinnell Attorney-Kinney, Alexander, Sell, Ste'ldt & Delahunt [5 7] ABSTRACT 3 Claims, No Drawings PROCESS FOR PRODUCING ON IMPREGNATED WATERLAID SHEET AND RESULTANT PRODUCT This invention relates to leather substitute materials. An aspect of this invention relates to insole and outsole material for shoes, boots, and similar wearing apparel. Another aspect of this invention relates to a waterlaid sheet of leather fibers impregnated with a cured in situ elastomeric polyurethane (or polyurea) composition.

For the shoe manufacturer and the consuming public, natural leather has been and still is synonymous with high quality insofar as footwear (particularly shoe insoles, outsoles, uppers, heels, and the like) is concerned. Natural leather (e.g., calfskin, steerhide, side leather, and similar epidermal or hide materials) is considered to'have a remarkable combination of proper ties: for example, ease of fabrication (good stitch tear and tongue tear resistance and easy shaping or lasting, good internal bond or strength (dry peel back resistance), and good wearing properties (resistance to compression set, abrasion resistance, flex fatigue resistance, etc.). The consuming public associates even the appearance, odor, and feel of leather with quality insole and outsole material and generally overlooks the disadvantages of leather, e.g., rapid water pickup (which may cause discomfort) and high density.

Accordingly, for a leather substitute to be preferable to natural leather in the high quality insole and outsole market, it would have to mimic the advantages and characteristics of leather while eliminating the disadvantages. The prior art approaches to making an artificial sole material have generally involved the use of a rubbery polymer alone or in combination with a fibrous filler or web, the fibrous material being either synthetic (e.g., nylon, polyester, etc.) or natural (wool, cotton, leather dust, cork, etc.). When a rubbery polymer or elastomer per se is used, the resulting sole material generally has very specialized uses (e.g., tennis shoes, work shoes, and the like) due to the lack of leather-like characteristics. When natural or synthetic fibers (or other fillers) are combined with an elastomer, the resulting sole material may be more leather-like in many respects, but may also share the disadvantages of leather. Most prior art elastomer/fiber leather substitutes are made from a mixture of fibrous filler and an elastomeric binder and/or by a process wherein a cloth or a non-woven material (e.g., an airor waterlaid web) is impregnated and/or coated with a polymer. A good summary of the prior art is found in U.S. Pat. No. 3,116,200 (Young et al.) issued Dec. 31, 1963. Examples of prior art techniques are found in the following U.S. Pat. Nos. 3,255,061 (Dobbs) issued June 7, 1966; 3,102,835 (White) issued Sept. 3, 1963; 2,973,284 (Semegen) issued Feb. 28, 1961; 2,769,712 (Wilson) issued Nov. 6, 1956; 3,034,927 (Fairclough et al.) issued May 15, 1962; 2,697,048 (Secrist) issued Dec. 14, 1954; 2,723,935 (Rodman) issued Nov. 15, 1955; 2,721,811 (Dacey et al.) issued Oct. 25, 1955; 2,719,806 (Nottebohm) issued Oct. 4, 1955; and 3,051,612 (Bennett) issued Aug. 28, 1962. See also German Pat. No. 1,220,384, published July 7, 1966.

in practice, it is extremely difficult to both imitate and improve upon the properties of natural leather with fiber/polymer materials. For example, in selecting the fiber-to-polymer ratio, it is necessary to avoid using too much polymer in order to avoid unduly accentuating the rubbery properties of the polymer at the expense of the leather-like properties provided primarily by the fiber. If too much fiber is used, the internal strength of the resulting leather substitute will tend to be strikingly inferior to natural leather. This is particularly true when leather fiber is included in the fiber/polymer material. In Raymond et al., U.S. Pat. NO. 3,436,303, issued Apr. 1, 1969, the patentees teach that a sample containing 60 percent fiber and 40 percent polymer was a loose fibrous porous material. Furthermore, it can be quite difficult to maintain uniformity of the fiber-to-polymer ratio throughout the structure.

In optimizing prior art fiber/polymer sheet materials, it is almost always desirable to provide low apparent density (high void volume); however, this desideratum must be balanced against the likelihood of rapid liquid water pickup and poor internal strength or high compression set. This is particularly true when the fiber is leather fiber. Since leather has an affinity for water, the rate of water pickup would be expected to be rapid when leather fiber is used in a fiber/polymermaterial. High void volume (low apparent density) can also speed up the rate of water, pickup, because sponge-like structures (e.g., those of U.S. Pat. No. 2,977,330 (Brower), issued Mar. 28, 1961) have a large capacity for water.

Furthermore,'a high void volume is difficult to maintain; it tends to be markedly decreased by processes, materials, or treatments which improve internal bond strength. (Low density waterlaid sheets require, as a rule, reinforcing, heating, and/or pressing, while airlaid sheets containing a substantial amount of leather.

fiber are generally too flimsy to be made into insole or outsole materials.) Other problems arealso created by such treatments or processes. Reinforcing or binding a leather fiber sheet with solution polymers generally calls for a relatively low molecular weight, linear polymer system for high solubility of the polymer and low viscosity of the solution. Another drawbackis that migration of the polymer impregnant tends to occur while the solvent is evaporating, resulting in a nonuniform fiber/polymer ratio. The use of emulsified polymer systems is complicated by the nonuniform penetration of larger emulsoid particles (above 0.1 micron) and the salt content and pH characteristics of leather fibers. As with solution systems, polymer migration can occur during drying.

Void volume is particularly likely to be sacrificed when pressing and/or large amounts of'binder are used to achieve a good internal bond. Large amounts of saturant tend to fill up voids, and pressing reduces the number and/or size of the voids. To illustrate: a typical fiber/polymer sheet containing a substantial amount of leather fiber has a true density (density at 0 percent void volume) ofiat least 1.1 g/cc and generally greater than 1.2 g/cc. If a void volume of at least 20 percent could be achieved and maintained, the sheet could have an apparent density lower than 0.9 g/cc, a significant improvement over natural leather and many types of synthetic outsole materials. (However, the danger of more rapid water pickup must always be borne in mind.) But pressed sheets often have 20 percent voids.

Despite all the aforementioned difficulties, leather fiber has striking aesthetic and economic advantages for use as a filler or fibrous component in a shoe sole material; for this reason a leather-fiber/polymer sheet with low. apparent density, low compression set, slow water pickup, good internal strength, etc., is still being sought by industry.

Accordingly, this invention contemplates providing a sheet material from natural leather fiber and a rubbery binder wherein: pressing or other densification of the sheet and the amount of rubbery binder in the sheet are kept to a minimum, thereby maintaining a high void volume; both desirable leather-like properties and the amount of leather fiber in the sheet are maximized, thereby taking full advantage of the aesthetic appeal and properties of leather; the rate of water pickup of the sheet is made as slow as possible, so that upon brief immersions in liquid water, only a minor amount of the voids will take up liquid water; the internal bond of the sheet is maximized; the permanent compression set of the sheet is minimized; and the method of making the sheet is designed such that strict control over all of the aforementioned properties is possible. This invention also contemplates a substantially uniform impregnation of awaterlaid sheet with a rubbery binder which can be non-linear and/or relatively high in molecular weight.

Briefly, this invention involves:

l. Forming a waterlaid sheet (or batt or fiber cake) from an aqueous slurry of fibrous material, at least onethird, preferably at least two-thirds, of this material being leather fiber,

2. Mixing together a free isocyanate-containing material and an active hydrogen-containing material, (wherein active hydrogen is defined according to the Zerwitinoff test, J. Amer. Chem.'Soc. 49, 3181 (1927) with or without suitable solvents, catalysts, or the like, and

3. impregnating the aforementioned dry waterlaid sheet with the mixture of starting materials described previously before 7 these starting materials have interacted to any great extent. It is possible to combine the mixing and impregnating steps (Steps (2) and (3) provided the resulting impregnation is both complete and uniform. However, to. achieve the outstanding quality control which is an important feature of this invention, it is not desirable to impregnate the preformed waterlaid sheet with either unmixed starting materials (i.e., with seriatim impregnation steps) or with starting materials that have been in admixture for a period of time sufficient to allow total curing or even a substantial amount of curing prior to impregnation.

The uncured impregnant can undergo an exothermic in situ cure in the waterlaid sheet at ambient temperatures, e.g., C. or higher. For maximum control over internal bond strength, uniformity of impregnation, and water pickup, substantially all of the curing (chain propagation including chain extension, branching, and crosslinking) should be in situ, i.e., after impregnation, rather than during the mixing step, and the uncured impregnant should contain at least about 20 wt. percent solvent. If the starting materials of the impregnant are dissolved in a solvent, removal of the solvent from the waterlaid sheet can be accomplished by drying at room temperature or, preferably, at suitable elevated temperatures. Solvent removal should not be begun until the in situ cure is substantially completed. Afterthe in situ cure of the impregnant is complete,

pressing of the resulting sheet material is generally not The term denotes a paper-like sheet having a small thickness (relative to the area) and comprising solids which have been deposited from an aqueous slurry or the like onto a foraminous surface, e. g., onto the screen of a handsheet mold or Fourdrinier machine.

Leather-like sheet materials made according to this invention have a substantially uniform fiber/polymer ratio throughout their thickness. The thickness, for outsole materials or heels can be up to 2 or 3 cm or more; typically, 6 or 9 Iron (0.32 or 0.48 cm) sheets make good sole materials. Lamination can be used to increase the thickness still further, and splitting can be used to reduce the thickness to, for example, a millimeter. The process of this invention is inherently capable of producing, without lamination, sheets about 0.5 -l .0 cm in thickness. In this context, the term substantially uniform means'that, in the innermost regions or core areas of the impregnated and cured sheet produced by this invention (which will normally be 0.5-l cm thick), the fiber/polymer ratio is substantially the same as that of the areas or regions near (within a millimeter of) the exposed surfaces of the sheet, differences or variations in this ratio between such core and near-surface regions being substantially less than 20 percent and preferably less than 10 percent. (it may be desirable to have a higher fiber/polymer ratio at one or more surfaces of the sheet to provide a leather-like skin.) The apparent density of sheets made according to this invention can be less than 1.0 g/cc, and apparent densities as low as 0.3 g/cc have been achieved in practice. To provide a noticeable advantage over natural leather, the apparent density should be well below 1.4 g/cc, and preferably below 1.2 g/cc. An internal bond strength (dry peel back) substantially greater than 10 pounds per lineal inch 1,800 g. per lineal cm) can be obtained according to the teachings of this invention. The theoretical void volume of sheets of this invention can be as high as 80 percent, but preferably is less than percent. For low apparent density, the 'void volume should be at least 20 percent. Of the total apparent volume of a sheet made according to'this invention, about 15 to about 35 percent will be closed, or substantially closed, cells. As a generalrule, roughly one-half to two-thirds of the total void volume will be closed cells having elastomeric walls-certainly more than 15 or 20 percent of the total void volume will be closed cells-but the desirable properties of sheets made according to this invention are apparently not entirely dependent upon water repellent and internal bonding effects caused by such closed cells. A substantial portion of the void volume of sheets of this invention, e.g., more than one-third, can be open or intercommunicating cells without adversely affecting the desired properties. The permanent compression set (ASTM test B-2213-cT) of the cured sheet is less than about 25 percent and is preferably less than 15 percent. The fiber/polymer ratio (by weight)-of the cured sheets ranges from 0.4:1 to 1.7:], preferably about 1:1, and the particular fiber-to-polymer ratio for a particular sheet will have the substantial uniformity described previously. (Expressed in terms of polymer-to-fiber ratio, this range is 0.6:l2.5:l, and preferably about 1:1.) The flex fatigue resistance or flex life of sheets of this invention is determined by cutting a hole in a sample sheet and flexing it on a Ross Rubber Flexing Machine (Emerson Apparatus Co., Melrose, Mass). Samples are conditioned at 50 percent relative humidi ty and 23 C. before the Ross flex test. The flex life of preferred sheets of this invention is in excess of 30,000 cycles.

A particularly advantageous feature of cured sheets made according to this invention is the slow water pickup rate. The expression water pickup rate, as used herein, means the percent of water absorbed at room temperature by an initially dry sample in a given increment of time. The percent of water absorbed can be expressed as either weight percent (based on the weight of a dry sample) or volume percent (based on the apparent volume of a dry sample). For ease of calculation, all measurements are in grams and cubic centimeters, and the density of water at room temperature is assumed to be exactly one gram per cc. If W is the weight of the dry sample and W is the weight of the sample after immersion in a room temperature water bath, the weight percent water absorption will be given by:

The volume percent absorption is obtained by multiplying the above expression by the apparent density, assuming the density of water is 1.00 g/cc.

In determining the water pickup rate, 30 minutes is a particularly meaningful time increment, insofar as insole and outsole material is concerned. Fora 30-minute immersion, representative water pickup rates of sheets made according to preferred embodiments of this invention are less than wt. percent and are generally less than 5 wt. percent, even though such sheets have a void volume greater than 20 percent and contain a significant amount of leather fiber. The 2-hour rate is less than 20 wt. percent and generally less than 10 wt. percent for these preferred materials. Surprisingly, the 24- hour rate is stillless than three-fourths (and can be less than half) of the theoretical absorptive capacity of the sheet. This slow penetration of water can readily be appreciated by comparing the rate of pickup in volume percent with the theoretical void volume of the sheet. As a practical matter, this means that an outsole made from a sheet of this invention could be in contact with a wet pavement or wet ground for long periods of time without picking up a significant amount of water. And this effect can be achieved without the use of waterproofing additives.

lt is difficult to explain this slow water pickup phenomenon in view of the high void volume (which can include a substantial number of open or intercommunicating cells) and highleather fiber content of the sheets of this invention. Although this invention is-not bound by any theory, it is theorized that what appears to be open or interconnected cells in air pycnometer tests of the cured sheets are actually quite resistant to. absorption of liquid water. This resistance to water is, however, not characteristic of similar porous materials, e.g., the sheet material described in the aforementioned Raymond et al. U.S. Pat. No. 3,436,303. It is further theorized that all, or nearly all, of the leather fibers in the sheet are coated with polymer and thus rendered hydrophobic.

Nor can it be explained precisely how the cell structure of this invention is obtained. It is theorized that the uncured impregnant wets outthe leather fibers and cures on the surface of the fibers. The formation of closed cells may thus be a partially chemical and partially physical phenomenon. Direct bonding between active hydrogen-bearing substituents present in the leather particles or fibers and free isocyanate containing molecules is believed to occur.

As pointed out previously, at least one-third and preferably two-thirds, by weight, of the fiber used in practicing this invention should be leather fiber of paper-making length (less than about 15 mm and preferably less than 5 mm). The natural leather fibrous material can be chrome or vegetable tanned and can be dyed and/or pigmented. The leather fiber can be slurried with a discontinuous (e.g., chopped staple) synthetic fiber such as polyamide, regenerated cellulose or cellulose acetate (e.g., rayon), polyolefin (e.g., polyethylene or polypropylene), polyester (e.g., polyethylene terephthalate and acetal copolymers), etc. Naturally occurring staple fibers such as wool and cotton (or other natural cellulosic fibers) can also be used. Such natural or synthetic staple fiber is preferably one to six denier and preferably shorter than 15 mm. in length. To maximize the aesthetic and desirable physical properties of natural leather, the amount of natural or synthetic fiber other than leather should be kept to less than 10 wt. percent and preferably less than 5 wt. percent of-the total fiber content of the sheet. Surprisingly, these lower synthetic fiber content materials have a slower water pickup rate. Needless to say, it is within the scope of this invention to add modifying ingredients other than the aforementioned fibers, e.g., mineral fillers or fibers such as glass or asbestos. It is permissible, but not necessary, to add chemical agents, dyes or pigments to the aqueous slurry prior to the formation of the waterlaid sheet of fiber, provided that these agents, e.g., anionic surfactants and the like, do

not contain either active hydrogen (as defined by the Zerwitinoff test) or free isocyanate. It is both unnecessary and undesirable to add elastomeric binder materi-' als or other thermoplastic resins, polyisocyanates, or prepolymers to the aqueous fibrous slurry prior to the formation of the waterlaid sheet.

Elastomeric binder-forming materials used in the practice of this invention are not introduced into the sheet until after formation and drying of the fibrous waterlaid sheet is complete. The preferred binder material, after curing, comprises a polyurethane (including polyurethane-polyurea) or'polyurea elastomer containing --NHRNHCO- and X-Z-X CO units, and preferably -XZ XCO units,

in the polymer chain, wherein R is a divalent aliphatic,

aralkylene, or aromatic group such as an alkylene radi-..

cal of four to 10 carbon atoms or a monocyclic or polycyclic aromatic or aralkyl nucleus such as benzene, toluene, xylene, diphenylmethane, naphthalene, etc.; X is O, S, NH, N-aliphatic, or the like; Z is a polyoxyalkylene or polyester chain; and Z is a divalent aliphatic, cycloaliphatic, or aromatic radical. Although these units are shown as divalent structures, it should be understood that, if a crosslinked, crosslinkable, branched-chain polyurethane is desired, the Z, Z "or R groups can have one or more additional substituents. The Z radical is derived from a compound having the formula Z (XH),,,, wherein Z and X are as defined previously, m is 1-5, preferably 2 or 3, and H is an active hydrogen as defined previously; Z (XH), can be piperazine and the like. In the preferred polymers, X is oxygen or NH. If the Z chains in the molecule are not the same, i.e., the polymer contains more than one kind of polyoxyalkylene and/or polyester chain, at least one 2 chain preferably has a molecular weight of at least about 400 but less than about 5 ,000.

When 2 is a polyester chain, the polyester units are preferably of the repeating formula OA O COA CO, wherein A and A are divalent aliphatic groups such as alkylene radicals. These polyester units can be derived from the interaction of a bifunctional initiator with one or more lactones, for example, as described in U.S. Pat. No. 2,933,477, or by an esterification or ester-interchange reaction involving a dicarboxylic acid or anhydride or ester thereof with an alkylene polyol, preferably an alkylene glycol.

When polyesters are prepared from dicarboxylic acids, anhydrides, or esters, and alkylene glycols, the

preferred acid, anhydride, or ester, can be selected from a wide variety of polybasic (preferably dibasic) acids. It is preferred to use the dibasic fatty acids, i.e.,

e.g., 1-8. Particularly suitable dibasic acids are malonic, succinic, and adipic. Examples of useful alkylene glycols are ethylene glycol; 1,3-propane-diol; 1,4-butane diol, and the like.

It is possible to modify the stiffness of the polymer by introducing in the polyurethane-forming reaction various chain-extending, chain-branching, or chain-terminating agents, e.g., arylene diamine chain extenders. A particular advantage of this invention is the freedom of using tri or higher functionality materials to achieve crosslinking in the resultant finished sheet material. Preferred chain-branching agents are the triols and triamines commonly used in the polyurethane art. .Chain propagation can be carried out in any suitable manner know in the art, e.g., the one shot procedure, which generally involves the use of a catalyst, or the chain-extension of a suitable prepolymer. Prepolymers are preferred. The preferred components are: an aromatic diisocyanate, an active hydrogen component comprising a polyoxyalkylene glycol and an aromatic diamine, and, optionally, one or more compounds having 3-5 active hydrogen-bearing substituents (e.g., a triol), and a suitable catalyst, e.g., an organo-metallic compound such as stannous octoate, mercuric acetate, phenyl mercuric acetate, or the like. Polyoxyalkylene diamines can be substituted for the polyoxyalkylene glycol with good results. An advantage of this substitution is that the resulting polyurea can be more degradation resistant. Water and/or carboxyl containing compounds can be included in the active hydrogen component, but due to the formation of carbon dioxide, such inclusion is ordinarily not preferred.

The molecular weight, cross-link density (if any), amount of aromatic content (if any), amount of urea and/or urethane linkages, etc., of the polyurethane or polyurea binder material must be selected such that the binder is elastomeric in nature. By elastomeric is meant the ability of an article, e.g., a cast film consisting of the polymer, to be elongated substantially more than percent of its length and to return with force to substantially the original length. Elastomeric polymers suitable for use in this invention have a molecular weight greater than 10,000 and form films with the following physical properties: (tested free of fillers and the like at 23 C. and 50 percent relative humidity) a tensile strength of at least 300 (21.1 Kg/cm) psi, preferably at least 750 psi (52.8 Kg/cm a stress at 100 percent elongation of at least 50 psi (3.5 Kglcm preferably at least psi (10.5 Kglcm and an elongation at break of at least 300 percent, preferably at least 500 percent. To avoid undue stiffness, the stress at 100 percent elongation should not exceed 1,000 psi (70 Kg/cm). To avoid undue rubberiness, the elongation at break should not exceed 1,500 percent. v

As pointed out previously, the elastomeric binder materials of this invention are preferably formed by mixing the starting materials in the presence of a volatile organic liquid solvent or vehicle (i.e., a solvent for the uncured starting materials, not necessarily the fully cured polymer) and a suitable catalyst to form a low viscosity saturant system with which the waterlaid sheet is saturated. The starting materials interact primarily while in situ, i.e., in the sheet. When a suitable catalyst is'included in the saturant mixture, curing of the mixture can be completed at ambient temperatures near roomtemperature, e. g., 20-25 C. Since the curing reaction-is exothermic, the use of ordinary ambient temperatures is preferred; however, ambient tem'- peratures up to 65 C. can be used. If the starting materials are of sufficiently low viscosity, the use of a solvent can be avoided. However, some solvent (ordinarily at least 20 wt. percent) is preferably always used in order to control the final polymer/fiber ratio. Suitable solvents include esters such as ethyl acetate and butyl acetate, ethers such as tetrahydrofuran and dioxane, ketones such as acetone and methylisobutylketone (but, with ketones, Schiffs base reactions must be considered), sulfones, hydrocarbons (particularly aromatic hydrocarbons such as toluene) sulfoxides, chlorinated hydrocarbons, and mixtures of one or more of these. Organic liquids can, if desired, be selected from the-above list with a view toward low toxicity and/or miscibility with water. After the in situ cure is substantially complete, the organic liquid solvent can be evaporated or drawn off from the cured, impregnated sheet at ambient temperatures near room temperature or at elevated temperatures, e.g., up to 70 C., and at atmospheric or subatmospheric pressure. The aromatic hydrocarbons (benzene, toluene, xylene,

etc.) are particularly suitable for removal from the cured sheet. A possible explanation for this might be because they have little, if any, affinity for the fully cured polymer.

Prior to impregnation with the elastomeric binderforrning impregnant, a waterlaid sheet of fiber is made according to standard papermaking techniques using a Fourdrinier screenor a hand sheet mold. This waterlaid sheet is substantially self-supporting and has sufficient strength after drying to pennit further processing. The sheet is saturated with the impregnant by any suitable method including immersion in, floating upon, or spraying with the impregnant. The preferred method (hereinafter referred to as float saturation) is to float the sheet upon a bath of the impregnating agent. As pointed out previously, the starting materials which make up the impregnant are preferably premixed prior to the impregnation step. The time lapse between mixing up the impregnant and commencing the saturation of the waterlaid sheet should not be unduly long, however. With some systems, a lapse of up to 2 hours is not too detrimental, but the lapse should preferably be as short as possible, e.g., less than minutes, preferably less than 5 minutes. The time lapse can be reduced to zero by spraying the waterlaid sheet with two sprayheads, one dispensing an active hydrogen-containing component and the other dispensing the free isocyanate component. The two sprays intermingle in the interstices of the sheet, thus combining the impregnating and mixing steps of this invention.

Although the preceding description has been directed primarily toward using the impregnated waterlaid sheet of this invention as insole or outsole material, heels, and other elements of footwear, other uses will occur to the skilled technician. Amongthese uses are pads for abrasive-surfaced discs, backup layers for dyecutting, gaskets, furniture, conveyor belts, and any other use where a tough, leather-like sheet or laminate is needed.

In the following nonlimiting Examples, all parts are by weight unless otherwise specified. Weight percent and apparent volume percent pickup are determined as described previously. Theoretical percent void volume is determined by 100 X (1.27 apparent density)/1.27, since 1.27, on the average, is the true density of the solid material (leather and polyurethane) in the sheets made according to these Examples.

EXAMPLE 1 A dyed pigmented leather fiber sheet was prepared as follows: Chrome tanned leather fibers (Lorum Fiber Co. Y-020-015 chrome tanned leather fibers) were beat up with water using a Vally paper beater (Vally Iron Works). A 6.3 wt. percent total solids leather fiber slurry was obtained having an S.R. (Schopper-Riegler) freeness of l9.5. One hundred thirty-eight grams of leather solids (2,190 grams of slurry) was diluted to liters in a S-gallon 17.9 liters) pail with cold tap water. The diluted slurry was added to a 12 X 12 inch (30.5 X 30.5 cm) Williams Apparatus Co. handsheet mold. The slurry was drained catching the fibers on the wire. The resulting waterlaid sheet was then removed and dried in a 150 F. (66 C.) forced air oven.

The two-part polyurethane impregnant system was as follows:

Two hundred parts of a Part -A (composed of 712 parts of a 2,000 molecular weight polyoxypropylene glycol, 43.2 parts of methylenebisorthochloroaniline, 4.3 parts phenylmercuric acetate, 32.0 parts of an amorphous silica filler with particle size of approximately 0.1 micron (available under the trademark Cab-O-Sil from Cabot Corp.), 3.0 parts of a mull of 80% PbO,(by wt.) in a 2,000 molecular weight polyoxypropylene glycol, 2.40 parts of calcium octoate and 3.2 parts of 2,6-ditertiary butyl paracresol), and

Sixty parts of a Part B prepolymer (composed of 30.6 parts of a 400 molecular weight polyoxypropylene diol and 8.7 parts of a 435 molecular weight polyoxypropylene triol reacted with 60.7 parts of /20 [by wt.] isomer mixture of 2,4l/2,-toluenediisocyanate at 66 C. for approximately 4 hours).

Parts A" and B were mixed with 482 parts toluene and poured into a 8% X 12 inch (21.5 X 30.5 cm) glass tray immediately after mixing. Within a minute after this pouring step, a 6 X 12 inch (15.25X 30.5 cm) piece of the above described dried, waterlaid sheet of leather fiber was submerged in this bath and saturated. After about an hour an immobile gel formed. The impregnated sheet was removed, the excess polymer scraped from its surface, followed by drying at F. (66 C.). The dried sheet looked very much like leather.

The finished sheet had the following properties:

Polymer-to-fiber ratio: 0.91:1 Apparent density 0.56 g/cc Theoretical void volume 56 Dry peel back resistance (peel back rate l ft/min or 30.48

Thus, after 24 hours, less than half of the theoretical void volume had taken up water.

Similar results can be obtained by maintaining the impregnating conditions of this Example and using the float saturation technique, wherein the sheet is floated on the surface of the higher-density, uncured impregnant liquid.

EXAMPLE 2 In this Example, the effect of varying the amount of saturant solids was investigated.

Several dyed pigmented leather fiber sheets were prepared by beating up chrome tanned leather fibers (Lorum Fiber Co. Y-020-0l5 chrome tanned leather fibers) in water with a paper beater. The leather fiber slurry was refined until it had a S.R. freeness of 19. Then 7.5 lb. (3,420 g.) of these solids were diluted, in a chest, with water wash to obtain a 3 percent slurry. Enough of this was added to a 20 X 20 inch (50.8 X 50.8 cm) handsheet mold so as to have about 1,000 grams of solids per sheet of material. The water was drained from the handsheet mold filtering out the fibers on a wire grid. Each waterlaid sheet was rubber dammed by placing a thin sheet of latex film over the still-wet waterlaid sheets and removing the air from below so as to further remove water. The sheets were dried at 200 F. (93 C.) for 8 hours. The dried waterlaid sheets were all approximately 0.4 inch (1.0 cm) thick, having an apparent density of approximately 0.3 g/cm. Example 2(A): 35 wt. percent Solids Saturant The saturant was: 158 parts of a Part A (composed of 3,560 parts of a 2,000 average molecular weight polyoxypropylene glycol and 216 parts methylenebisorthochloroaniline) mixed with 50.4 parts of the same Part B described in Example 1, 388 parts toluene, and 3.12 parts of a 30 wt. percent solution, in aqueous ammonia, of phenylmercuric acetate catalyst (Metasol 30, trademark of Metal Salts Corp., l-lawthrone, N.J.). An 8 X 8 inch (20.3 X 20.3 cm) piece of the above described dried waterlaid sheet was then float saturated as described in Example 1; the sheet was allowed to gel; and the excess polymer was scraped from its surface, followed by drying at 150 F. (66 C Example 2(8): 45 wt. percent Solids Saturant Another sheet was prepared by the procedure of Example 2(A) and with the same materials except that the following saturant formulation was used:

204 parts of Part A 65.5 parts of Part 8" 330 parts of toluene 2.47 parts of the catalyst solution of Example 2(A). Example 2(C): 55 wt. percent Solids Saturant Another sheet was prepared using the same procedure and materials as in Example 2(A) except the following saturant formulation was used:

250 parts of Part A 80 parts of Part 8" 270 parts of toluene 1.82 parts of the catalyst solution of Example 2(A) Example 2(D): 65 wt. percent Solids Saturant Again still another sheet was prepared using the same procedure and materials as Example 2(A) except the following saturant formulation was used:

295 parts of Part A" 94.6 parts of Part B 210 parts of toluene 1.17 parts of the catalyst solution of Example 2(A) Example 2( E): 70 wt. percent Solids Saturant Finally a fifth sheet was prepared using the same procedure and materials as in Example 2(A) except the following saturant formulation was used:

318 parts of Part A 101 parts of Part B 179 parts of toluene 1 0.84 part of the catalyst solution of Example 2(A).

The above five sheets were evaluated with the following results tabulated:

TABLE I Formulation and Properties 180 Dry Peel Back measured (3600 g/cm) Wt. 11,0 pick-up aher 30 min. submer Approx. Volume Example sion at 20-25 C. pickup, 30 min., 20-25 C.

EXAMPLE 3 In this example, up to 50 percent by weight of the A dry waterlaid sheet was prepared from dyed, pig-.

mented leather fiber by the same procedure as in Example 2. The saturant system was 200 parts of the Part A of Example 1 mixed with 60 parts of the Part B of Example 1 and 482 parts toluene. The above sheet was float saturated" followed by placing in a press with warm plattens. heated to a temperature in the range of 50-60 C., between release liners, under very moderate pressure (only enough to hold the sheet perfectly flat). During this time gellation occurs, after which the sheet is removed and dried at 150 F. (66 C.). Example 3(8): wt. percent Leather/25 wt. percent Rayon A dyed, pigmented 75 percent 1eather/25 percent rayon fiber dry waterlaid sheet was prepared by the same process as in Example 2 except that 25 percent of the leather was replaced with one-quarter inch (0.63 cm) long X 2 denier rayon fiber. This sheet was then float saturated, pressed, and dried as in Example 3(A). Example 3(C): 50 wt. percent Leather/50 wt. percent Rayon A dyed, pigmented 50 percent leather/50 percent rayon fiber dry waterlaid sheet was prepared by the same process as in Example 2 except that 50 percent of the leather was replaced with one-quarter inch (0.63 cm) long by 2 denier rayon fibers. This sheet was then float saturated, pressed and dried as in Examples 3(A) and 3(8).

The following tabulated data are the results of the evaluation of Examples 3(A) 3(C).

' TABLE 111 Example 3(A) 3(8) 3(C) Polymer to Fiber Ratio 0.8 1/1 1.17/1 1.10/1 Density, flcm 0.57 0.55 0.47 180 Dry Peel Back 7 lb/in. 13 lb/in. 8 lb/m.

' (1200 g/cm) (2300 g/cm) (1400 g/cm) Flex Cycles to Failure 50,000 50,000 7,500 (Ross" Flex Test) 50,000 41,000 19,000 Compression Set 17% 14% v 16% Wt. of Fiber Leather 75 50 Wt. of Fiber Rayon 0 '25 50 Sample conditioned at 50% relative humidity and 23 C. for 1 week second flex value for each of Examples 3(A)-3(C) is a duplicate run. "ASTM test 8-2213-63T TABLE IV Theoretical Void Volume vs. Water Pickup In every case the 24-hour water pickup, by volume, was less than half of the theoretical void volume. However, the sheets with 75 wt. percent or more of leather fiber were more water resistant and had better flex life and internal strength.

EXAMPLE 4 This example illustrates the uniformity of the polymer-to-fiber ratio throughout the impregnated waterlaid sheet.

A dry waterlaid sheet was prepared from dyed, pigmented leather fiber as in Example 2. An 8 X 12 inch (20.3 X 30.4 cm) piece of this dry sheet was float saturated and dried at 66 C. as described in Example 1.

153.2 parts of the Part A described in Example 2 46.8 parts of the Part B described in Example 2 200 parts of toluene 1.45 parts 30 wt. solution of phenylmercuric acetate (see Example 2(A) The resultant sheet was then split into 1 1 layers, each as near as possible to 30 mils (0.076 cm) thick, numbered l-l 1 from top to bottom.

Assuming the leather fiber to have a constant percent ash (run at 1,000 C.), ash values were run on each of the l 1 layers to show uniform polymer distribution. The following results were obtained: (Nos. 2-10 were similar in appearance and density.)

TABLE V Layer No. Wt. Ash

Top:

Bottom As is apparent from this data, a very uniform polymer distribution is achieved.

EXAMPLE 5 orthochloroaniline, both of which are dissolved in toluene at 55.5 percent solids) was mixed with 243.9 parts of a Part B (a prepolymer prepared by reacting 1,000 parts of a 1,000 molecular weight, hydroxyl terminated poly(epsilon-caprolactone) with 348 parts 80/20 mixture 2,4-/2,6-isomers of toluene diisocyanate in toluene at 52.9 percent solids for 4 hours at C 27.6 parts of toluene and 0.75 g. of a 30 wt. percent solution of phenylmercuric acetate (see Example 2(A) An 8 X 8 inch (20.3 X 20.3 cm.) piece of the abovedescribed waterlaid sheet was float saturated as described in Example 1. The excess gel was removed followed by drying at 150 F. (66 C. as in Example 1.

The resultant sheet was rigid in comparison to those described in previous examples. I

It was found to have an apparent density of. 0.63 g./cc. The water pickup, by weight, was 3.6 percent after 30 minutes submersion.

EXAMPLE 6 A leather fiber waterlaid sheet was prepared by the same procedure as in Example 2 except that enough crimped one-quarter inch (0.64 cm) X 2 denier nylon fibers were added to fiber slurry to equal 3 percent of the total leather fiber weight. The following saturant formulation was used:

153.2 parts of a Part A (same as used in Example 2) mixed with 468 parts of a Part B" (same as used in Example 2) and 200 parts of toluene. To this mixture 1.45 parts of a 30 wt. percent solution of phenylmercuric acetate catalyst (see Example 2(a) was added and stirred in. The resulting saturant mixture was then added to a glass tray and a 20.3 X 20.3 cm piece of the above waterlaid sheet was float saturated as described in Example 1. The saturant was allowed to gel without the loss of solvent. The excess gel was scraped from the surface of the sheet followed by drying at 66 C.

The resultant sheet had the following properties:

Polymer-to-fiber ratio: 0.93:1 Apparent density: (40% theo. void vol.) 0.76 g/cc 180 dry peel back: 16 lbs/in (2800 g/cm) H O pickup afier 30 minutes submersion: 3.4 wt.

EXAMPLE 7 A polyether urea Part B was prepared diluting 1,000 parts of a 2,000 molecular weight polyoxypropylene diamine with 1,000 parts of toluene. One hundred seventy-four parts of (/20 [wt.] mixture 2,4-/2,6-isomers) toluene diisocyanate was diluted with 174 parts toluene also. The polyether diamine solution was then added to the toluene diisocyanate solution with agitation. The mixture was allowed to exotherm and then cool to room temperature.

A Part A was prepared by dissolving parts of methylene-bis-orthochloroaniline in 200 parts of dimethylformamide.

60.0 parts of the above Part A was mixed with 388.0 parts of the above Part B. To this mixture, 0.75 part of a 30 wt. per cent solution of phenylmercuric acetate (see Example 2(A) was added and stirred in. This saturant mixture was added to a tray in which an 8 X 7 inch (20.3 X 17.8 cm) piece of a waterlaid sheet of leather fiber (as prepared in Example 2) was float saturated as in Example 6. The saturant mixture was allowed to gel without the loss of solvent. The excess gel was removed and the sheet was dried at 66 C as in Example 6. The resultant sheet had the following Apparent density: (46% theo. void vol.) Water pickup after 30 minutes submersion: 180' dry peel back:

' 0.69 glen 3.4 W1. l lbs/in (I800 g/cm.)

As will be apparent to the skilled technician from a review of the preceding Examples, elastomeric binders containing polyoxypropylene chains (see the 2* term, defined previously) have the advantage of providing a relatively flexible impregnated and cured sheet wherein the leather content has somehow been made at least partially hydrophobic. Similar advantages, at slightly greater cost, can be obtained with other polyoxyalkylene (Z chains wherein the alkylene portion of the oxyalkylene units contains at least three carbon atoms, e.g., poly(oxy-l,2-butylene), poly(oxy-l ,4-butylene), etc. Oxyethylene units are not preferred, due to their relatively high hydrophilicity.

What is claimed is:

1. A process for preparing an impregnated fibrous sheet comprising:

1. forming a paper-like fibrous sheet at least 1 mm. in thickness by depositing a mass of fibers, said fibers comprising at least one-third by weight of leather fiber,

2. mixing together a curable liquid impregnant system comprising a. a polyisocyanate,

b. a compound containing a polymeric chain selected from the group consisting of a polyester chain and a polyoxyalkylene chain, said compound further containing at least two active hydrogen-bearing substituents, and

c. a chain propogating agent containing at least two active hydrogen-bearing substituents, and

d. an organic solvent,

3. impregnating said fibrous sheet uniformly throughout its thickness with said curable liquid impregnant system less than 2 hours after said mix 4. substantially preventing loss of said solvent from said curable liquid impregnant system and from said fibrous sheet at least until said curable liquid impregnant system has cured in situ in said fibrous sheet to a stage at which said curable liquid impregnant system has become a substantially immobile, gel-like solid, and

5. removing said solvent by evaporation after said step (4) is completed.

2. A process according to claim 1 wherein said impregnating is commenced less than 10 minutes after said mixing.

3. An impregnated fibrous sheet made according to the process of claim 1.

a s s a a Patent Na. 3,7 ,333 hater? January 2, 1973 Inventg3(g) Robert C. Carlson It is certified that error appears in the above-irlentified patent and that said letters Patent are herehy ctrrectecl as shown below:

In the Title, at the end of the first line, change "ON" to AN 5 Column line 63, change the ASTM Test number at the beginning of the line to properly read Column 10, line 5, change. "2, 41" to 2,4- so that the ratio reads: 2, l-/2,6-toluenediisocyanate and line 21, change "0.91:1" to 0.9:1

being the "Polymer-to-fiber ratio"; and

Column 12, line 63 (last line of Table III), insert the figure "25 as the last line of Column 3(3); in other words, move it over to the left so that "50" in column 3(C) stands alone.

Signed and sealed this 29th day of May 1973.

Attest; I

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attes'ting Officer Commissioner or P31261115 ORM FO-lOSO (10-69) 

2. mixing together a curable liquid impregnant system comprising a. a polyisocyanate, b. a compound containing a polymeric chain selected from the group consisting of a polyester chain and a polyoxyalkylene chain, said compound further containing at least two active hydrogen-bearing substituents, and c. a chain propogating agent containing at least two active hydrogen-bearing substituents, and d. an organic solvent,
 2. A process according to claim 1 wherein said impregnating is commenced less than 10 minutes after said mixing.
 3. An impregnated fibrous sheet made according to the process of claim
 1. 3. impregnating said fibrous sheet uniformly throughout its thickness with said curable liquid impregnant system less than 2 hours after said mixing,
 4. substantially preventing loss of said solvent from said curable liquid impregnant system and from said fibrous sheet at least until said curable liquid impregnant system has cured in situ in said fibrous sheet to a stage at which said curable liquid impregnant system has become a substantially immobile, gel-like solid, and
 5. removing said solvent by evaporation after said step (4) is completed. 